Prospective Study of Placental Angiogenic Factors and Maternal Vascular Function Before and After Preeclampsia and Gestational Hypertension

Is inflammation the cause of pre-eclampsia?

It has been proposed that either excessive inflammation or an imbalance in angiogenic factors cause pre-eclampsia. In the present review, the arguments for and against the role of inflammation and/or angiogenic imbalance as the cause of pre-eclampsia are discussed on the basis of the Bradford–Hill criteria for disease causation. Although both angiogenic imbalance and systemic inflammation are implicated in pre-eclampsia, the absence of temporality of inflammatory markers with pre-eclampsia challenges the concept that excessive inflammation is the cause of pre-eclampsia. In contrast, the elevation of anti-angiogenic factors that precede the clinical signs of pre-eclampsia fulfils the criterion of temporality. The second most important criterion is the dose–response relationship. Although such a relationship has not been proven between pro-inflammatory cytokines and pre-eclampsia, high levels of anti-angiogenic factors have been shown to correlate with increased incidence and disease severity, hence satisfying this condition. Finally, as the removal of circulating sFlt-1 (soluble Fms-like tyrosine kinase receptor-1) from pre-eclamptic patients significantly improves the clinical outcome, it fulfils the Hill's experiment principle, which states that removal of the cause by an appropriate experimental regimen should ameliorate the condition. In contrast, treatment with high doses of corticosteroid fails to improve maternal outcome in pre-eclampsia, despite suppressing inflammation. Inflammation may enhance the pathology induced by the imbalance in the angiogenic factors, but does not by itself cause pre-eclampsia. Development of therapies based on the angiogenic and cytoprotective mechanisms seems more promising.

The elevation in circulating anti-angiogenic factors is independent of markers of neutrophil activation in preeclampsia

Background

Severe preeclampsia is associated with increased neutrophil activation and elevated serum soluble endoglin (sEng) and soluble Flt-1 (sFlt-1) in the maternal circulation. To dissect the contribution of systemic inflammation and anti-angiogenic factors in preeclampsia, we investigated the relationships between the circulating markers of neutrophil activation and anti-angiogenic factors in severe preeclampsia or systemic inflammatory state during pregnancy.

Methods and results

Serum sEng, sFlt-1, placenta growth factor, interleukin-6 (IL-6), calprotectin, and plasma α-defensins concentrations were measured by ELISA in 88 women of similar gestational age stratified as: severe preeclampsia (sPE, n = 45), maternal systemic inflammatory response (SIR, n = 16) secondary to chorioamnionitis, pyelonephritis or appendicitis; and normotensive controls (CRL, n = 27). Neutrophil activation occurred in sPE and SIR, as α-defensins and calprotectin concentrations were two-fold higher in both groups compared to CRL (P < 0.05 for each). IL-6 concentrations were highest in SIR (P < 0.001), but were higher in sPE than in CRL (P < 0.01). sFlt-1 (P < 0.001) and sEng (P < 0.001) were ≈20-fold higher in sPE compared to CRL, but were not elevated in SIR. In women with sPE, anti-angiogenic factors were not correlated with markers of neutrophil activation (α-defensins, calprotectin) or inflammation (IL-6).

Conclusions

Increased systemic inflammation in sPE and SIR does not correlate with increased anti-angiogenic factors, which were specifically elevated in sPE indicating that excessive systemic inflammation is unlikely to be the main contributor to severe preeclampsia.

Angiogenic factors and the risk of adverse outcomes in women with suspected preeclampsia

BACKGROUND

An imbalance in circulating angiogenic factors plays a central role in the pathogenesis of preeclampsia.

METHODS AND RESULTS

We prospectively studied 616 women who were evaluated for suspected preeclampsia. We measured plasma levels of antiangiogenic soluble fms-like tyrosine kinase 1 (sFlt1) and proangiogenic placental growth factor (PlGF) at presentation and examined for an association between the sFlt1/PlGF ratio and subsequent adverse maternal and perinatal outcomes within 2 weeks. The median sFlt1/PlGF ratio at presentation was elevated in participants who experienced any adverse outcome compared with those who did not (47.0 [25th-75th percentile, 15.5-112.2] versus 10.8 [25th-75th percentile, 4.1-28.6]; P<0.0001). Among those presenting at <34 weeks (n=167), the results were more striking (226.6 [25th-75th percentile, 50.4-547.3] versus 4.5 [25th-75th percentile, 2.0-13.5]; P<0.0001), and the risk was markedly elevated when the highest sFlt1/PlGF ratio tertile was compared with the lowest (odds ratio, 47.8; 95% confidence interval, 14.6-156.6). Among participants presenting at <34 weeks, the addition of sFlt1/PlGF ratio to hypertension and proteinuria significantly improved the prediction for subsequent adverse outcomes (area under the curve, 0.93 for hypertension, proteinuria, and sFlt1/PlGF versus 0.84 for hypertension and proteinuria alone; P=0.001). Delivery occurred within 2 weeks of presentation in 86.0% of women with an sFlt1/PlGF ratio ≥85 compared with 15.8% of women with an sFlt1/PlGF ratio <85 (hazard ratio, 15.2; 95% confidence interval, 8.0-28.7).

CONCLUSIONS

In women with suspected preeclampsia presenting at <34 weeks, circulating sFlt1/PlGF ratio predicts adverse outcomes occurring within 2 weeks. The accuracy of this test is substantially better than that of current approaches and may be useful in risk stratification and management. Additional studies are warranted to validate these findings.

The sFlt-1/PlGF ratio in different types of hypertensive pregnancy disorders and its prognostic potential in preeclamptic patients

OBJECTIVE

The soluble fms-like tyrosine kinase (sFlt-1)/placental growth factor (PlGF) ratio is a reliable tool in the assessment of preeclampsia. We tested the hypothesis that the sFlt-1/PlGF ratio is able to identify women at risk for imminent delivery. We characterized the sFlt-1/PlGF ratio in different types of hypertensive pregnancy disorders.

STUDY DESIGN

We investigated 388 singleton pregnancies with normal pregnancy outcome, 164 with PE, 36 with gestational hypertension, and 42 with chronic hypertension. sFlt-1 and PlGF were measured in serum samples.

RESULTS

Patients with preeclampsia had a significantly increased sFlt-1/PlGF ratio as compared with controls and with patients with chronic and gestational hypertension in <34 weeks and ≥34 weeks (P < .001). Time to delivery was significantly reduced in women with preeclampsia in the highest quartile of the sFlt-1/PlGF ratio (P < .001).

CONCLUSION

The sFlt-1/PlGF ratio allows the identification of women at risk for imminent delivery and is a reliable tool to discriminate between different types of pregnancy-related hypertensive disorders.

Circulating anti-angiogenic factors during hypertensive pregnancy and increased risk of respiratory distress syndrome in preterm neonates

OBJECTIVE

To test the hypothesis that high circulating concentrations of maternal anti-angiogenic factors are associated with increased risk of respiratory distress syndrome (RDS).

STUDY DESIGN

This is a nested case-control study of nulliparous women who delivered less than 37 weeks of gestation within the Calcium for Preeclampsia Prevention (CPEP) trial. The study included 116 women with preeclampsia or gestational hypertension and 323 normotensive controls. Soluble fms-like tyrosine kinase 1 (sFlt1), placental growth factor (PlGF) and soluble endoglin (sEng) in maternal serum were measured at 21-32 weeks of gestation.

RESULTS

Preterm infants born to hypertensive mothers were more likely to develop RDS (22.5% vs. 20.9%, p = 0.03). After adjustment for gestational age at delivery, the odds ratio for the relationship between hypertension in pregnancy and RDS was 2.18 (95% CI 1.08-4.39). In hypertensive pregnancies women whose infants developed RDS had significantly higher circulating mean sFlt1 levels during midpregnancy (21-32 weeks of gestation) even after adjustment for gestational age at delivery (21,516 pg/mL vs. 7,000 pg/mL, p = 0.01).

CONCLUSIONS

Preterm preeclampsia and gestational hypertension, characterized by high circulating levels of sFlt1, are associated with a twofold increased risk of RDS in infants delivered before 37 weeks. Among women with these hypertensive pregnancies circulating sFlt1 concentrations during midpregnancy were substantially higher in women whose infants developed RDS.

Prevention of vascular dysfunction after preeclampsia: a potential long-term outcome measure and an emerging goal for treatment

Preeclampsia is increasingly being recognised as more than an isolated disease of pregnancy. In particular, preeclampsia has emerged as an independent risk factor for maternal cardiovascular disease and has recently been recognised as a risk factor for cardiovascular disease in children exposed in utero. Preeclampsia and cardiovascular disease may share important pathophysiological and molecular mechanisms and further investigation into these is likely to offer insight into the origins of both conditions. This paper considers the links between cardiovascular disease and preeclampsia and the implication of these findings for refinement of the management of patients whose care is complicated by preeclampsia.

The vascular marker soluble fms-like tyrosine kinase 1 is associated with disease severity and adverse outcomes in chronic heart failure

OBJECTIVES

We sought to evaluate placental growth factor (PlGF) and soluble Fms-like tyrosine kinase 1 (sFlt-1) as clinical biomarkers in chronic heart failure (HF).

BACKGROUND

Vascular remodeling is a crucial compensatory mechanism in chronic HF. The angiogenic ligand PlGF and its target receptor fms-like tyrosine kinase 1 modulate vascular growth and function, but their relevance in human HF is undefined.

METHODS

We measured plasma PlGF and sFlt-1 in 1,403 patients from the Penn Heart Failure Study, a multicenter cohort of chronic systolic HF. Subjects were followed for death, cardiac transplantation, or ventricular assist device placement over a median follow-up of 2 years.

RESULTS

The sFlt-1 was independently associated with measures of HF severity, including New York Heart Association functional class (p < 0.01) and B-type natriuretic peptide (p < 0.01). Patients in the 4th quartile of sFlt-1 (>379 pg/ml) had a 6.17-fold increased risk of adverse outcomes (p < 0.01). This association was robust, even after adjustment for the Seattle Failure Model (hazard ratio: 2.54, 95% confidence interval [CI]: 1.76 to 2.27, p < 0.01) and clinical confounders including HF etiology (hazard ratio: 1.67, 95% CI: 1.06 to 2.63, p = 0.03). Combined assessment of sFlt-1 and B-type natriuretic peptide exhibited high predictive accuracy at 1 year (area under the receiver-operator characteristic curve: 0.791, 95% CI: 0.752 to 0.831) that was greater than either marker alone (p < 0.01 and p = 0.03, respectively). In contrast, PlGF was not an independent marker of disease severity or outcomes.

CONCLUSIONS

Our findings support a role for sFlt-1 in the biology of human HF. With additional study, circulating sFlt-1 might emerge as a clinically useful biomarker to assess the influence of vascular remodeling on clinical outcomes.

Threshold of soluble fms-like tyrosine kinase 1/placental growth factor ratio for the imminent onset of preeclampsia

It has not been clarified whether thresholds of soluble fms-like tyrosine kinase 1 (sFlt-1), placental growth factor (PlGF), soluble endoglin, and the sFlt-1/PlGF ratio for the imminent onset of preeclampsia (PE) exist. We hypothesized that onset thresholds for the imminent onset of PE could be determined by the distributions of these 4 markers just after the onset of PE. Study subjects were 51 PE after the onset of PE; 36 of PE, 20 of gestational hypertension, 142 of a small-for-gestational-age infant, and 400 of normal pregnant controls at 19 to 25 and 27 to 31 weeks of gestation in a prospective cohort study. The current data supported our hypothesis that onset thresholds of sFlt-1 and the sFlt-1/PlGF ratio exist. The onset thresholds of the sFlt-1/PlGF at 26 to 31 weeks of gestation were useful for detecting imminent PE with the onset at <36 weeks of gestation, showing sensitivity of 0.36 and a positive likelihood ratio and 95th percent CIs of 38 (11-132); when positive, PE occurred at 2.2±0.6 weeks (range: 1.4-3.0 weeks) after the measurement of the sFlt-1/PlGF ratio. The combination of sFlt-1 at 26 to 31 weeks of gestation, past history of gestational hypertension or PE, prepregnancy body mass index, and mean blood pressure at 16 to 23 weeks of gestation was useful for detecting PE with onset of <36 weeks of gestation, showing sensitivity of 0.82, and a positive likelihood ratio (95% CI) of 42 (20-88). In conclusion, the onset threshold of sFlt-1/PlGF existed and might be useful for detecting the imminent onset of PE.

Levels of soluble fms-like tyrosine kinase one in first trimester and outcomes of pregnancy: a systematic review

Angiogenic factors are involved in formation of new blood vessels required for placental development and function; and critical for fetal growth and development. Soluble fms-like tyrosine kinase 1(sFlt-1) is an anti-angiogenic protein that inhibits formation of new blood vessels resulting in potential pregnancy complications. The objective of this study was to undertake a systematic review to assess levels of sFlt-1 in early pregnancy and association with adverse pregnancy outcomes. PubMed and Medline databases and reference lists were searched up to July 2010. Inclusion criteria were pregnant women, blood sample taken during first trimester and assessment/reporting of sFlt-1 concentrations and subsequent pregnancy complications. Twelve relevant studies were identified of 71 to 668 women. No pooling of results was undertaken due to variation in sFlt-1 concentrations (range, 166-6,349 pg/ml amongst controls), samples used (serum, plasma), different summary statistics (mean, median, odds ratio) and outcome definitions applied. Levels of sFlt-1 were generally higher among women who developed preeclampsia (11 studies) or gestational hypertension (two studies), but not significantly different to normotensive women in most studies. There was no consistent pattern in association between sFlt-1 concentrations and fetal growth restriction (4 studies); and levels were non-significantly higher for women with postpartum bleeding (1 study) and significantly lower for stillbirths (1 study).This review found no clear evidence of an association between sFlt-1 levels in first trimester and adverse pregnancy outcomes. However, findings were affected by methodological, biological and testing variations between studies; highlighting the need for consistent testing of new biomarkers and reporting of outcome measures.

Disrupted balance of angiogenic and antiangiogenic signalings in preeclampsia

The placenta plays a central role in governing local circulatory system that mediates maternal condition and fetal growth. In early gestational phases, the placenta exerts properties of invasion and neovascularization for successful placentation. Extravillous invasive trophoblasts replace uterine endometrial vasculature and establish local blood pathway to obtain oxygen and nutrients from the mother. In later phases, the placenta promotes villous angiogenesis and vascular maturation that are finely controlled by angiogenic and antiangiogenic molecules. Among various molecules involved in placental neovascularization, vascular endothelial growth factor receptors (VEGFRs) and angiotensin II receptor type 1 (AT1) mediate important signaling pathways for maternal circulatory system and fetal growth. VEGFR1 and VEGFR2 are functional receptors for placental growth factor (PlGF) and VEGF, respectively, and PlGF-VEGFR1 and VEGF-VEGFR2 interactions are disturbed in many preeclamptic patients by excess amount of soluble form of VEGFR1 (also named sFlt1), a natural PlGF/VEGF antagonist. Recent studies have disclosed that excessive sFlt1 production in the placenta and aberrant AT1 signaling in the mother are closely associated with the pathology of preeclampsia and intrauterine growth restriction (IUGR). In this paper, neovascularization of the placenta and pathological events associated with disrupted balance between angiogenic and antiangiogenic signaling in preeclampsia are discussed.

The origins and end-organ consequence of pre-eclampsia

Pre-eclampsia is a multisystem disorder with profound implications for both mother and fetus. Its origins lie in the earliest stages of pregnancy. Abnormal interactions between fetal trophoblast and maternal decidua, including the cells of the maternal immune system, lead to inadequate placental invasion and maternal vascular remodelling. However, abnormal placentation is only one step in the cascade of events that ultimately result in maternal organ dysfunction. Pre-existing maternal conditions predisposing to inflammation and vascular pathology, fetal factors, including multiple gestations and macrosomia, and environmental exposures, including infection, may contribute to the release of placental substances, including anti-angiogenic molecules, into the maternal circulation. These may act directly or indirectly upon the endothelia of end organs, including the kidney, liver and brain. The liberation of reactive oxygen species, cytokines, and microthrombi from damaged endothelia contribute further to organ damage. In studying the normal processes that occur during human placentation and early pregnancy, we will develop a greater understanding of what may go awry in pre-eclampsia. Such research will be crucial in discovering novel biomarkers for prediction of the disorder and, eventually, in finding targets for effective interventions.

Financial impact of a novel pre-eclampsia diagnostic test versus standard practice: a decision-analytic modeling analysis from a UK healthcare payer perspective

OBJECTIVE

Pre-eclampsia (PE), a leading cause of maternal and perinatal morbidity and mortality, is only detected after symptomatic onset. Early diagnosis may be possible with a new serum test, with resulting clinical and economic benefits versus standard practice. The authors evaluated the financial impact to the UK National Health Service (NHS).

METHODS

A decision-analytic model was developed in which a cohort of 1,000 pregnant women receiving UK obstetric care was simulated. The economic impact of improved sensitivity and specificity of the novel PE test [Roche Diagnostics, Rotkreuz, Switzerland] over current diagnostic practice was modeled. While there is no specific approved diagnostic test to detect PE, physicians are using a combination of tests including blood pressure, proteinuria, Doppler, serum uric acid, etc. The novel PE test constitutes two novel biomarkers Placenta Growth Factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) which can be quantitatively analyzed using an automated system widely available in hospitals or laboratories (Elecsys/Cobas, Roche Diagnostics) and measures the levels of PlGF and sFlt-1 growth factors in pregnant women. The analysis assumed administration of the £31.13 test (the equivalent of 52 Swiss Francs [CHF]) after 20 weeks of gestation as an addition to current practice. True-positive and false-negative patients were assumed to develop mild or severe PE, eclampsia, or death. A hybrid research approach was adopted; when available, data for model inputs were obtained from published literature and public databases. Interviews with obstetricians, laboratory managers, and healthcare payers were used to validate model inputs and fill utilization-related data gaps.

RESULTS

The model estimates that the costs associated with managing a typical pregnancy are £1,781 per patient when the new test is used versus £2,726 with standard practice. This represents savings of £945 per pregnant woman, if the test is used as a supplementary diagnostic tool. The savings are attributed to the new test's improved performance and its ability to better classify the pregnant patients.

CONCLUSIONS

The novel test has the potential to provide substantial cost savings for NHS. Even when the novel test's cost is added to the current cost of care, the benefits exceed the additional cost, driven by the test's ability to reduce the rates of false-positive and false-negative diagnoses compared to current standard of care. Potential study limitations include the use of a pooled average of the individual sensitivities and specificities of currently used tests since no data were available on combination testing, the reliance on clinical trial data versus actual practice, and the use of clinical expert opinion when published data were unavailable.